Case Study of ASICs

Case Study

Sun Microsystems released the SPARCstation 1 in April 1989. It is now an old design but a very important example because it was one of the first workstations to make extensive use of ASICs to achieve the following:

• Better performance at lower cost
• Compact size, reduced power, and quiet operation
• Reduced number of parts, easier assembly, and improved reliability

The SPARCstation 1 contains about 50 ICs on the system motherboard—excluding the DRAM used for the system memory (standard parts). The SPARCstation 1 designers partitioned the system into the nine ASlCs shown in Table 1.1 and wrote specifications for each ASIC—this took about three months 1 . LSI Logic and Fujitsu designed the SPARC integer unit (IU) and floating-point unit ( FPU ) to these specifications. The clock ASIC is a fairly straightforward design and, of the six remaining ASICs, the video controller/data buffer, the RAM controller, and the direct memory access ( DMA ) controller are defined by the 32-bit system bus ( SBus ) and the other ASICs that they connect to. The rest of the system is partitioned into three more ASICs: the cache controller , memory-management unit (MMU), and the data buffer. These three ASICs, with the IU and FPU, have the most critical timing paths and determine the system partitioning. The design of ASICs 3–8 in Table 1.1 took five Sun engineers six months after the specifications were complete. During the design process, the Sun engineers simulated the entire SPARCstation 1—including execution of the Sun operating system (SunOS)............

TABLE 1.1 The ASICs in the Sun Microsystems SPARCstation 1.
SPARCstation 1 ASIC		Gates (k-gates)
1	SPARC integer unit (IU)	20
2	SPARC floating-point unit (FPU)	50
3	Cache controller	9
4	Memory-management unit (MMU)	5
5	Data buffer	3
6	Direct memory access (DMA) controller	9
7	Video controller/data buffer	4
8	RAM controller	1
9	Clock generator	1

Table 1.2 shows the software tools used to design the SPARCstation 1, many of which are now obsolete. The important point to notice, though, is that there is a lot more to microelectronic system design than designing the ASICs—less than one-third of the tools listed in Table 1.2 were ASIC design tools.

TABLE 1.2 The CAD tools used in the design of the Sun Microsystems SPARCstation 1.
Design level	Function	Tool 2
ASIC design	ASIC physical design	LSI Logic
	ASIC logic synthesis	Internal tools and UC Berkeley tools
	ASIC simulation	LSI Logic
Board design	Schematic capture	Valid Logic
	PCB layout	Valid Logic Allegro
	Timing verification	Quad Design Motive and internal tools
Mechanical design	Case and enclosure	Autocad
	Thermal analysis	Pacific Numerix
	Structural analysis	Cosmos
Management	Scheduling	Suntrac
	Documentation	Interleaf and FrameMaker

The SPARCstation 1 cost about $9000 in 1989 or, since it has an execution rate of approximately 12 million instructions per second (MIPS), $750/MIPS. Using ASIC technology reduces the motherboard to about the size of a piece of paper—8.5 inches by 11 inches—with a power consumption of about 12 W. The SPARCstation 1 “pizza box” is 16 inches across and 3 inches high—smaller than a typical IBM-compatible personal computer in 1989. This speed, power, and size performance is (there are still SPARCstation 1s in use) made possible by using ASICs. We shall return to the SPARCstation 1, to look more closely at the partitioning step, in Section  15.3, “System Partitioning.”